Feature 5 | FPSO TECHNOLOGY
Easier riser and umbilical connections for FPSOs
Brian Green, general manager, First Subsea, explains how diverless bend stiffener connectors are assisting FSPO operators to connect risers without the assistance of diver teams or ROVs, as the increased number of tiebacks to FPSOs becomes a common feature of oil and gas fields.
F
loating production, storage and offloading (FPSO) vessels are playing an increasingly strategic
role as processing and storage hubs in the development of remote oil and gas fields. It’s a trend that looks set to grow significantly over the next five years, if the latest forecasts by industry analysts are to be believed. Te need to tie back more fields to the FPSO is prompting the development of diverless and remotely operated vehicle (ROV)-less, compact, flexible riser connections. In locations with stable weather systems,
risers are normally connected to the side of the FPSO. However where there is a storm or hurricane risk, submerged turret production (STP) buoys are preferred. These allow the buoy to be abandoned while the FPSO moves to a safe port, and later retrieved once the storm has passed. In both cases, there has been a steady increase in the number of flexibles that need to be tied back to the FPSO. Flexible risers either connected to
a subsea riser base or the turret exit of an FPSO are subject to dynamic environmental loads that cause the riser to flex about a fixed location. Tis movement,
in combination with large
axial loads, results in overbending and fatigue, causing damage to the riser structure. Bend stiffeners prevent this by providing localised stiffness to the flexible, thus limiting the bending stresses and curvature to acceptable levels. Typically a bend stiffener is a conically
shaped, polyurethane moulding. Up to 12m in length and weighing in excess of 5tonnes, each bend stiffener comprises a conical external profile, cylindrical tip section, and smooth bore to suit the external diameter of the riser. Connecting the bend stiffener (and riser) can be a time consuming and hazardous business, especially when divers are involved in securing the bend
28
The Type II DBSC used in the Neptune Deep Water Project North and South, off the Massachusetts coastline.
stiffener connection. Moreover the installation is dependent upon good weather to complete the operation. One way round the problem is to use a diverless bend stiffener connector (DBSC). Te concept of the DBSC enables a fully
integrated riser connector design that maximises the engineering performance of both the stiffener and connector elements. It is optimised for each project with respect to the bending moments and load path analysis, system finite element analysis (FEA) and fatigue analysis. Unlike other bend stiffener connection
technologies which use external locking mechanisms and hydraulic pressure to hold the bend stiffener in place, the DBSC uses a ball and taper type connection which
works on the simple principle of a ball engaged in a taper. Te male connector is inserted within a female receptacle or I/J tube. As the male connector’s balls roll up the receptacle’s wall, tapers drive the balls outwards and the tightness of the grip increases in direct proportion to the load applied. The connector is self-aligning and self-energising, enabling it to be fitted and secured in position without the need for divers, making the installation safer and quicker.
Connection integrity In its simplest form the DBSC can be fitted within an existing I/J tube and bellmouth during tieback to a FPSO. The Type I DBSC uses a ROV ‘hot stab’ hydraulic
Offshore Marine Technology 4th Quarter 2011
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32